Process of producing potassium sulphate



Sept. 8, 1942. 0. A. BUTT ET AL 7 ,2

PROCESS OF PRODUCING POTASSIUM SULPHATE Filed Dec. 15, less M0 mm sup/ 1r OF LIQUOR 570mm,: ZAA/GBEl/V/Tf M/XED SALTS STORAGE 5 VA PORA 70RWASTE MOTHER LIQUOR M 6M W INVENTORS Patented Sept. 8, 1942 UNITED.S'TATES PATENT OFFICE PROCESS OF PRODUCING POTASSIUM SULPHATE CharlesA. Butt, Atlanta, Ga., and Jacob Frank, Carlsbad, N. Mex, assignors toInternational Agricultural Corporation, New York, ,N. Y., a corporationof New York Application December 15, 1938, Serial No. 245,892

Claims.

This invention relates to the treatment of potassium bearing doublesalts for .the purpose of recovering potash therefrom. in carrying outthis invention a potassium containing double salt However, if half asmuch-K01 is used the reaction is:

3 (K 2S04.MgSO4) +MgCl2 The potassium magnesium sulphate mSOrMgSm can betreated with more potassium chloride thus:

It has been found in attempts to produce'potassium sulphate inaccordance with the above reactions, that if the theoretical amount ofpo tassium chloride is added to' langbeinite the reactions proceedslowly and may not be completed even after long periods of stirringthematerials in solution.

In accordance with the present'invention a considerable excess of KClover the theoretical amount needed may first be used for treating abatch of langbeinite. In this way practically all of the MgSOs of thatbatchis converted into MgCl2 in a short time as the reaction proceeds tocompletion. About excess to about 35% drawn from the potassium sulphatecrystals contains a substantial amount of potash which would be lost ifit; were not recovered therefrom. The

result would be a low recovery, as sulphate of potash, of the totalamount of potash contained in the langbeinite and potassium chloridethat is used.

In order to avoidtoo great a waste of potassium in the mother liquorfrom which potassium sulphate is obtained by treating langbeinite withpotassium chloride this mother liquor is used by the present inventionto treat charges of langbeinite in succession in such a way that themother liquor'having a high K20 content contacts with langbeinite fromwhich a part of the MgSO4 has been removed, the mother liquor from thistreatment having a smaller K20 content contacts with langbeinite fromwhich a smaller amount of magnesium sulphate has been removed and so onin a succession of steps, until finally the mother liquor, substantiallyfree from K20, .is either discarded or is evaporated to recover theremaining m0 after its use in treating fresh lan'gbeinite. Three suchsteps have been found to be sumcient for the recovery of the majorportion of the potash from the mother liquors but five or possibly moresuchsteps are sometimes advisable.

The invention will be described in connection with an arrangement oftreating tanks and other apparatus diagrammatically illustrated in theaccompanying drawing in which the reference characters A, B, C, D and Eindicate a series of five treating tanks or agitators, legends indicateother apparatus, the numerals within circles indicate a sequence ofsteps that is followed after the process has started,'lines with arrowsindicate direction of movement of materials, and M. L. means motherliquor. It is to be understood that a valved pipe or other convenientmeans for transfer of liquids extends from the supply'of KCl solutionand also from the mother liquor storage to each tank A, B, C, D and Eand also from these tanks to the evaporator and from each tank to othertanks as needed for transferring mother liquor as described below for aseries of runs for production purposes, and

that each tank is provided with a stirrer or agitator and with heatingmeans.

In order to start the process each tank A, B,

i C, D and E is charged with pulverized langbeinite resulting magnesiumchloridemother liquor,

and there is added to tank A a suflicient amount of KCl aqueous solutionabove the theoretical amount needed, say about 25% excess, to convertsubstantially all oI-the magnesium sulphate in this tank into potassiumsulphate in about four hours or less. Water, or mother liquor fromprevious runs when .the same is available, is

from other runs is preferable to the water when available. The contentsof the tanks are stirred tank E, potassium chloride brine is fed to tankC, the mother liquor is removed from tank A (in pcsition E) andevaporated to recover salts, the mother liquor in tank D .(in positionC) is transand left to settle and after time enough has ferredto tank A,and mother liquor istransferred elapsed for the reaction -of the K01with the from the storage tank to tank D.

langbeinite to take place the following steps are For the next-run,which is the third run of the taken. cycle, the tanks are in effectmoved clockwise In order to start the process, equal amounts anotherstep and then the contents of tank C of langbeinite are added to thefive tanks. The now in A position) are removed and filtered to KClsolution that is added in excess to tank A separate the potassiumsulphate, immediately causes the reactions forming the potassiumsulthereafter langbeinite and mixed salts are fed to phate to becompleted within a reasonable time. tank C, the mother liquor in tankAistransferred Water in amount about equal to the K01 soluto tank C, themother liquor in tank D is transtion is added to each of the othertanks. ferred to tank A, potassium chloride brine is fed Step 1.--Thetotal contents of tank A are filtotank D, the other quor is removed fromtered, or centrifuged, to separate the potassium tank B and evaporatedto recover salts, the mothsulphate, which is then sent to a dryer andstorer liquor in ank E is transferred to tank B, and

' age, Th filtered mothe liquor i transferred mother liquor istransferred from the storage to the mother liquor storage tank. m tankto tank E.

Step 2. The same quantity of freshlangbein- For the next run, which isthe fourth run of the ite as was originally added to each' tank is addedcycle, the tanks are in effect moved clockwise anto tank A. The mixedsalts that are recovered other p and then e contents of tank D ew inStep 6 are added to tank A along with the in A position) are removed andfilteredtosepacharge of langbeinite in succeding runs. The e thePotassium Sulphate. be n e and treatment of a batch of langbeinite asdescribed mixed Salts e fed t0 the tank the mother above is aconvenientway of proceeding with the iq r in tank B is transferred to k D. thprocess. By the end of about the 10th batch, or mother liq n tank E stransferred to n cycle, the salts and mother liquors reach sub-Potassium chloride brine is fed to tank stantial equilibrium. Thebatches, or cycles are mother liquor is removed from tank C and eprepeated with continuous production of sulphate orat d to recoverSalts, the mother quor in tank of potash. A is transferred to tank 0,and mother liquor is Step 3.'Ihe mother liquor in tank D is transferredfrom the storage tank to tank'A. pumped or siphoned into tank A. For thenext run, which is the fifth run of the Step 4.The mother liquor in tankB is $5 cy e, the tanks are in effect moved another step pumped orsiphoned into tank D. and then the contents of tank E (now in A Step5.-KC1 solution, in amount equal only to position) are removed andfiltered to s p the theoretical quantity necessary to convert the thepotassium sulphate, langbeinite and mixed MgSOr contained in thelangbeinite to MgClz is salts are fed to tank E, the mother liquor intank added to tank B. 40 C is transferred to tank E, the mother liquorin Step 6.'I'he mother liquor from tank E is tank A is transferred tothe tank C, potassium pumped to the evaporator, concentrated, andfurchloride brine is introduced into tank A, the ther recovery of potashis made thereby, in the mother liquor is removed from tank D andevapform of mixed salts. orated to recover salts, the mother liquor intank Step 7.-The mother li uor in t k 0 i B is transferred to tank D,andmother liquor is pumped or siphoned into tank E. transferred from thestorage tank to tank B.

Step 8.The mother liquor in the storage tank is co p t s e Cycle o five111115, and the is pumped or siphoned into tank 0. next run is identicalwith the first rundescribed The process proceeds a follows t finishabove Where the eight steps are numbered and cycle, which is repeated aslong as desirable. described- For the next run, which is the second runor The Co p t y e 0f V runs With eight the cycle, the tanks A, B, C, D,and E are in steps in each run is also shown in the following effectmoved clockwise one step or position by table in which the horizontallines indicate the proper adjustment of the valves in the valved ps nthe p ve s o wh ch there are pipes mentioned above, and then thecontents of five to complete a Cycle. The sixth run would tank B areremoved and filtered to separate the be the same as the first one inthis table, the potassium sulphate, immediately thereafter langsevenththe same as the second, and so on as long beinite and mixed salts arefed to tank B, (which as the process is continued. Equilibrium is inFig. 1 of the drawing is then in the position of reached after severalcycles. In this table LBN tank A) the mother liquor in tank E (now in 00means langbeinite, ML means mother liqposition D) is transferred to tankB, the mother uor, MS means "mixed; salts, Evp" means liquor in tank C(in position B) is transferred to evaporator, and St. means storagetank."

Steps 1 2 a 4 5 s 1 s lstrun Filter K1504 LBNandMS ML from ML-lromKCLtoB. MLfromE ML from MLfromSt.to

from A. to A. D to A B to D. to Evp. 0 to E. 0. 2nd run Filter K2804 LBNand MS ML from ML from KCLto 0. ML fromA ML from MLfrom St. to

a from B. to B. E to B. 0 to E. to Evp. D to A. D. 3rd run Filter K2804LBNand MS ML from ML from KOLtoD. ML from ML from- MLfromSt. to om O. toC. A to C. D to A. to Evp. E to B. 'E. 4th run Filter K2804 LBNand MS MLfrom ML from KClto 12.. ML from 0 ML from MLlrom St. to

D. to D. B to D E to B. to Evp. A to O. A. 5th run Filter K1804 LBNandMS ML from ML from KCltoA.. MLfromD ML from MLfroin St. to

om to E. C to E A to C. to Evp. B to D. B.

It will be understood from the foregoing de. scription that aiter freshlangeinite is put in tank A and mother liquor from tank D is addedthereto. tank A assumes the position or status of tanks E, D, C and Bsuccessively, in which positions the mother liquor in contact with thelangbeinite is siphoned OR and replaced with mother liquor from someother tank .in such manner that, as the K20 content of the mother liquordecreases, the mother liquor successively meets solids having increasingcontent of langbeinite. Langbeinite is only added where a, tank is inthe status of tank A, and is treated with mother liquors ofprogressively increasing K20 content. Each of the five tanks issuccessively put through a certain series of steps from the first stepof feeding the charge of fresh langbeinite and mixed salts and motherliquor from D to the final step ,of treating with KCl solution and thenfiltering on K2804 crystals. For instance, after allowing the motherliquor from tank D containing only a small proportion of K20 to remainin contact with the solids consisting of fresh langbeinite and. mixedsalts for a certain period, this mother liquor is later siphoned ofi atE to the evaporator and is replaced with mother liquor from C, and so onthrough asuccession of treatments until the strong or fresh KC] solutionafter contact with langbeinite that has been largely exhausted isseparated by filtration to give K2804 crystals, and

a is sent to mother liquor storage.

It has been found in the practice of this process that by using theevaporator to concentrate the end mother liquor obtained from the seriesof tanks and returning the salts obtained therefrom to the system about96% or more of the potassium that was introduced into the system in thelangbeinite and the potassium chloride is recovered in the potassiumsulphate when the process is carried on with heating of the tanks in theA, B and C positions and cooling of the tanks inthe D and E positionswhen the connections are as shown on the drawing. Even without theevaporatoror recovery of potassium from the end mother liquor that isdrawn from tank E and without the heating of some tanks and cooling ofothers, about 85% of the total potassium is recovered.

A fresh charge of langbeinite passes through a series of steps, asfollows, after the process has been started:

Fresh langbeinite and mixed salts recovered from the evaporated motherliquor are introduced into the emptied tank A and treated with motherliquor from tank D which is practically exhausted with respect to KCl byreason of hav-.

ing already treated four batches of langbeinite of successively greaterconcentrations. Then tank A assumes the position of tank E and themother liquor'is drawn off to the evaporator. The slightly or partiallyexhausted langbeinite in tank A (now in tank E position) is then treatedwith mother liquor from tank C which is a solution less exhausted withrespect to KCl than the first as it had treated only three batches oflangbeinite of successively greater concentrations. Then tank A assumesthe position of tank D and the mother liquor is drawn off to the tank inthe A position. The twice partially exhausted langbeinite in tank A (nowin tank D position) is then treated with mother liquor fromtank B whichis a solution less exhausted with respect to KCl than the second as ithad treated only two batches of langbeinite of successively greaterconcentrations. Then tank A assumes the position of tank 0 and themother liquor is drawn ofl to the tank in theE position. The thricepartially exhausted langbeinite in tank A (now in tank C position) isthen treated with motor liquor from the mother liquor storage which is astronger solution with respect to KC] than the third as it had treatedonly one batch of thrice partially exhausted langbeinite. Then tank Aassumes the position of tank B and the mother liquor is drawn off totank D. The partially exhausted langbeinite in tank A (now in tank Bposition), after the four treatments just described, is then treatedwith a solution of KCl. The tank A then assumes its position A and thecontents thereof is transferred to the filter, thus completing the run.

The process is somewhat of the nature of a counter current process asthe-fresh langbeinite first comes into contact with nearly spent motherliquor and then progressively into contact with stronger mother liquor,or mother liquor having more KCl therein, while the KCl solution firstcomes into contact with nearly spent langbeinite and then progressivelyinto contact with less spent batches of langbeinite.

It has been found in practicing this process that while an excess ofabout 30% over the theoretical amount of KCl is needed in the first tankwhen starting the process in order to obtain a highly pure potassiumsulphate salt quickly, this excess K01 is not lost as it passes in themother liquor from the tank into which it is introduced into other tankswhere it reacts with batches of langbeinite that are less and less spentor contain more and more MgSOr. Although only the theoretical amount ofKCl is added after theprocess has been started, an excess of it ispresent in the .tank into'which it is introduced so that the desiredreaction does not require an excessive amount of time.

when it is desired to produce the mixed salt, sulphate of potashmagnesia KzSOaMgSOc, instead of potassium sulphate, E804, by thisprocess this can be done by decreasing the amount of KCl that isintroduced into tank B.

It has been found that it is not always necessary to use five tanks'oragitators as the langbeinite can be rapidly converted into potassiumsulphate by using three tanks provided the salts are separated from themother liquors between batches.

What is claimed is:

1. The process of producing potassium sulphate, which comprises treatinglangbeinite that has been largely exhausted with a solution of potassiumchloride, to produce potassium sulphate in solid form and a motherliquor containing magnesium chloride, separating potassium sulphate thusformed from the mother liquor, treating with said resulting motherliquor langbeinite that has been less exhausted thus producing more ofsaid largely-exhausted langbeinite and a difierent mother liquor,treating fresh langbeinite with said last named mother liquor to producemore of said less' exhausted langbeinite, withdrawing from the processthe mother liquor resulting from the said last named-treatment, concentrating and cooling said withdrawn mother liquor to crystallizepotash salts therein, separating said potash salts and returning thesame to the process with fresh langbeinite, and discard- -lng the motherliquor resulting from said concentrating and cooling step.

.2. The process in accordance with claim 1, in

which the solution of potassium chloride is in exthe magnesium sulphatein said langbeinite that has been largely exhausted into potassiumsuiphate and magnesium chloride.

3. The process in accordance with claim 1, in

- which the first step is carried out an an elevated 5. The process inaccordance with claim 1, in which; the first step is carried out at anelevated temperature and with an amount of a solution of potassiumchloride in excess of the theoretical amount needed to convert themagnesium sulphate in said langbeinite that has been largely exhaustedinto potassium sulphate and magnesium chloride and the mother liquor iswithdrawn from the fresh langbeinite after cooling.

JACOB FRANK. CHARLES A. BU'I'I.

